It has been common for incubators, such as are used in the "Ektachem".TM. brand of clinical analyzers manufactured by Eastman Kodak Co. since 1982, to use plastic evaporation caps that cover plastic slides after the latter are slid into place under the caps, for incubation. During the use of thousands of such incubators, over the years, there has never been a problem, until recently, of the sample liquid that is predeposited onto the slides, spotting also the under-surface of the evaporation cap positioned above it.
However, recent modifications in the design have recently caused, in some instances, such spotting to occur. Some of those modifications include coating the incubator rotor disk with "Marten Hardcoat", a ceramic/"Teflon".TM. based material, to reduce wear and carry-over of ammonia from ammonia-producing slides, and converting portions of the housing of the incubator from metal to glass-filled plastic, for savings in cost and weight. The latter change has featured plastic connecting members that mount the rotating incubator to a drive spindle. The spotting is highly objectionable because of the color shift in the white reflectance of the evaporation cap, a problem particularly when using translucent slide elements.
The obvious cause of the problem was thought to be one of inertia. The caps must be snapping down too hard onto the captured slide so as to cause residual liquid not yet absorbed by the slide, to "jump up". The solutions that were tried for this problem were: a) to prevent such snapping action by the cap, and/or b) to double the height of the cap under-surface above the slide to prevent the inertially-displaced liquid from reaching it. However, none of these solutions was found to be effective. In fact, we have surprisingly discovered that inertia is not the cause of the problem at all.
Hence, prior to this invention, there has been an unsolved problem of sample liquid deposited on plastic, liquid-absorbing slide test elements, also becoming deposited in small amounts on the undersurface of the evaporation cap disposed above the slide element when the latter is in an incubator.